<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>常量</title>
</head>
<body>
    <script>
        //let a=5;
        //a=10;
        //alert(a);

        const a=5;
        a=10;
        alert(a);
    </script>
</body>
</html>